Gastroesophageal reflux disease (GERD) is one of the most common chronic disorders in Americans, affecting 20% of the adult population. It causes heartburn and acid damage to the esophageal squamous epithelium (ESE). These symptoms and/or signs are of concern because they interfere with sleep and work, impairing productivity and quality of life; can cause erosions that progress to stricture and/or Barrett's esophagus, the latter a risk factor for cancer; and are costly to treat, generally requiring chroni acid- suppression with proton pump inhibitors (PPIs) whose U.S. costs run ~ $13.9 billion/year. Treatment with PPIs, however, is suboptimal, not only because of cost, but because of lack of symptom relief in a sizable population (25%) with the non-erosive form of GERD, as well as side effects that increase the risk of infections, including Clostridia difficile colitis, osteoporosis nd hip fracture, and hypergastrinemia that promotes gastric parietal cell hyperplasia and rebound hyperacidity making PPI withdrawal difficult. Therefore, alternative medical therapy for GERD is greatly needed, especially with agents that are safe, inexpensive, and effective in non-erosive reflux disease, the most common form of GERD. One method for treating GERD that remains untapped is by development of an agent that improves mucosal defense. One means of improving this defense is by improving the barrier function of ESE. Improvement of barrier function now appears feasible based on our understanding of how refluxed gastric acid attacks and damages ESE, leading to heartburn and erosive esophagitis. Acidic refluxates alter the tight junctions (TJs) that serve as barriers to the paracellular movement of luminal acid into ESE. Consequently, ESE of both erosive and non-erosive forms of GERD develop 'leaky' tight junctions, evidenced by low transepithelial electrical resistance (RT), high transepithelial fluorescein flux and dilated intercellular spaces on microscopy. Recently, we determined that the 'leaky' tight junctions in GERD were characterized by a selective reduction in claudin-4 and that these same physiologic pertubations were replicated in the HET-1A human esophageal squamous cell line. Specifically, HET-1A cells, when grown to confluence on permeable supports, lacked significant barrier function (undetectable RT and high fluorescein flux) and had low claudin-4 levels. Quercetin, a flavanoid widely available in plants and as an over-the-counter nutritional supplement, is known to raise claudin-4 levels and improve TJ barrier function in Caco2, an intestinal epithelial cell line. Therefore, we exposed HET-1A cells to quercetin and found that it raised claudin-4 and improved both barrier function and acid resistance of the TJ in vitro. Moreover, it did so at concentrations (5-10 ?M) that approximate those achievable in vivo. These observations combined with data demonstrating that in vivo quercetin reduces esophageal damage in a rat model of reflux esophagitis provides strong conceptual support for a mechanistic study testing the hypotheses that: 'Oral quercetin can increase claudin-4 levels in vivo in the claudin-4 deficient ESE in GERD and by so doing increase both its barrier function and acid resistance.' Based on the above, then, the specific aims of this proposal are to: (1) Determine if oral quercetin increases the expression of claudin-4 in ESE of GERD in vivo; and (2) Determine whether the increase in claudin-4 by oral quercetin is accompanied by improvement in the barrier function and acid resistance of ESE in GERD. The achievement of these aims would provide strong support for performance of a controlled clinical trial to determine the value of oral quercetin for the treatment of GERD.